Gasoline fuel composition, method for the preparation and use of such a composition

ABSTRACT

The disclosure includes a petrol fuel composition including at least 70 mass % of a petrol fuel and at least one viscosifying compound which can increase the dynamic viscosity of the petrol fuel to a dynamic viscosity value, at a temperature of 40° C. and at atmospheric pressure, which is equal to or greater than 10 mPa·s, preferably 100 mPa·s, and imparting thereto a rheofluidifying nature. This disclosure also includes a method for preparing a petrol fuel composition of this type and its use as fuel for the internal combustion engine of a motor racing vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Entry of International Application No. PCT/EP2013/077588, filed on Dec. 20, 2013, which claims priority to French Patent Application Serial No. 1262582, filed on Dec. 21, 2012, both of which are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a gasoline fuel composition and the method of preparation thereof. The present invention also relates to a method of supplying fuel to an internal-combustion engine.

BACKGROUND

In the context of the development of the formulation of competition petroleum products, in particular competition fuels of the Formula 1 type, one of the objectives is to determine the formulation that will allow the overall performance of the car to be improved. This performance is finally measured by the improvement in lap time for a given circuit.

Numerous studies have been conducted on competition fuels in order to improve engine performance. For high-power engines, and in particular for car competition engines, the main qualities desired for the fuels supplying a competition engine are:

-   -   a high net calorific value (NCV), whether based on volume or         weight. The NCV represents the quantity of energy comprised in a         given volume or weight of fuel. The higher this energy value,         the more heat it will be possible to extract from a drop of         fuel. It will then be possible for this thermal energy to be         converted subsequently by the engine into mechanical energy in         order to extract more power from it. For certain applications,         increasing the NCV per weight or volume unit will make it         possible to increase the range in the race and therefore reduce         the frequency of refuelling;     -   a high speed of combustion. The speed of combustion represents         the speed at which the flame front is propagated in the         combustion chamber. The speed of combustion allows the peak         pressure in the chamber to be reached more quickly during the         process of a combustion cycle, and has an effect on the quality         of the engine efficiency. An increase in the speed of combustion         makes it possible to reduce the duration of a combustion phase,         a crucial parameter in the search for power on high-revving         engines.     -   a high knock- and pre-ignition resistance with high “research”         octane number (RON) and high “motor” octane number (MON). If the         octane numbers are insufficient relative to the compression         ratio applied on the engine, the phenomenon of knock or         self-ignition of the fuel may appear, which may damage the         engine considerably and dramatically reduce its performance.     -   An optimized oxygen content.         However, up to now, few studies have had the aim of proposing a         fuel that improves vehicle performance.

SUMMARY

The aim of the present invention is to propose a novel gasoline fuel composition, in particular for competition, that overcomes these drawbacks. In particular, the invention proposes an alternative to the existing high-power gasoline fuel compositions, in particular to the gasoline fuel compositions for automobile competition (rallying, circuits) the characteristics of which, currently in force, are to be found in article 9.1 of the rules of the International Automobile Federation (Federation Internationale de l'Automobile, FIA) in annex J-Art 252, published on Nov. 11, 2010.

The present invention relates to a gasoline fuel composition comprising at least 70% by weight of a gasoline fuel and at least one viscosifying compound able to increase the dynamic viscosity of the gasoline fuel up to a dynamic viscosity value greater than or equal to 10 mPa·s, measured at a temperature of 40° C. and at atmospheric pressure, and endow it with a shear-thinning character. According to a particular embodiment, the composition has shear-thinning behaviour on application of a stress comprised between 100 and 1000 s⁻¹. According to another particular embodiment, the viscosifying compound is selected from the viscosifying compounds that are able to endow said composition with a thixotropic character.

According to a particular embodiment, the viscosifying compound is selected from the derivatives of the N-substituted ureas and N-substituted bis-ureas, symmetric or asymmetric, alone or in a mixture. In particular, the viscosifying compound is selected from the derivatives of the N-substituted bis-ureas, symmetric or asymmetric, alone or in a mixture.

According to a development, the viscosifying compound comprises at least one substituent borne by a nitrogen atom of a urea function of the viscosifying compound, said substituent being selected from the group consisting of the C₅ to C₁₀ monocyclic or polycyclic aromatic rings, C₅ to C₁₀ heterocyclic rings, optionally substituted with one or more linear or branched, saturated or unsaturated C₁ to C₁₀ hydrocarbon-containing chains, said chains optionally containing one or more heteroatoms selected from N, O and S. According to another development, the viscosifying compound comprises at least one substituent borne by a nitrogen atom of a urea function of the viscosifying compound, said substituent being selected from the group consisting of the linear or branched saturated or unsaturated, C₁ to C₂₄ hydrocarbon-containing chains, said chains optionally containing one or more heteroatoms selected from N, O and S.

According to a particular preferred embodiment, the viscosifying compound is represented by the following formula (1):

wherein R₁ and R₂ are identical or different and represent independently a group selected from the group consisting of:

-   -   linear or branched, saturated or unsaturated C₁ to C₂₄         hydrocarbon-containing chains, said chains optionally containing         one or more heteroatoms selected from N, O and S and/or one or         more C₅ to C₁₀ monocyclic or polycyclic aromatic rings, and     -   C₅ to C₁₀ monocyclic or polycyclic aromatic rings, C₅ to C₁₀         heterocyclic rings, optionally substituted with one or more         linear or branched, saturated or unsaturated C₁ to C₁₀         hydrocarbon-containing chains, said chains optionally containing         one or more heteroatoms selected from N, O and S.

According to another particular preferred embodiment, the viscosifying compound is represented by the following formula (2):

wherein: Y represents a group selected from the group consisting of:

-   -   C₅ to C₁₀ monocyclic or polycyclic aromatic rings, C₅ to C₁₀         heterocyclic rings, optionally substituted with one or more         linear or branched, saturated or unsaturated C₁ to C₁₀         hydrocarbon-containing chains, said chains optionally containing         one or more heteroatoms selected from N, O and S,     -   linear or branched, saturated or unsaturated C₁ to C₂₄         hydrocarbon-containing chains, said chains optionally containing         one or more heteroatoms selected from N, O and S,         R₃ and R₄ are identical or different and represent independently         a group selected from the group consisting of linear or         branched, saturated or unsaturated C₁ to C₂₄         hydrocarbon-containing chains, said chains optionally containing         one or more heteroatoms selected from N, O and S and/or one or         more C₅ to C₁₀ monocyclic or polycyclic aromatic rings.

Advantageously, Y represents a group selected from the group consisting of the C₅ to C₁₀ monocyclic or polycyclic aromatic rings, C₅ to C₁₀ heterocyclic rings, optionally substituted with one or more linear or branched, saturated or unsaturated C₁ to C₁₀ hydrocarbon-containing chains, preferably C₁ to C₄, said chains optionally containing one or more heteroatoms selected from N, O and S. Advantageously, R₃ and R₄ are identical or different and represent independently a group selected from the group consisting of linear or branched, saturated or unsaturated, cyclic or acyclic C₁ to C₂₄ hydrocarbon-containing chains, said chains optionally containing one or more heteroatoms selected from N, O and S in the form of one or more functions selected from the ether, ester, ketone, amine, amide, imine, thiol, thioether or thioester functions and/or one or more C₅ to C₁₀ monocyclic or polycyclic aromatic rings, preferably monocyclic aromatic C₅ or C₆, optionally substituted with one or more linear or branched, saturated or unsaturated C₁ to C₁₀ hydrocarbon-containing chains, preferably C₁ to C₄.

According to a development, R₃ and R₄ are identical or different and represent independently the —CH(R₆)COOR₇ group wherein: R₆ and R₇ are identical or different and are selected independently from the group consisting of C₁ to C₂₄ linear or branched, saturated or unsaturated, cyclic or acyclic hydrocarbon-containing chains, preferably C₁ to C₁₈, said chains optionally containing one or more C₅ to C₁₀ monocyclic or polycyclic aromatic rings, preferably C₅ or C₆ monocyclic aromatic, optionally substituted with one or more linear or branched, saturated or unsaturated, C₁ to C₁₀ hydrocarbon-containing chains, preferably C₁ to C₄.

According to another particular preferred embodiment, the viscosifying compound is represented by the following formula (3):

wherein: R₃ and R₄ are as described above and R₅ represents a group selected from the group consisting of the linear or branched C₁ to C₁₂ hydrocarbon-containing chains.

According to a development, the viscosifying compound has a molecular weight less than or equal to 2000 g·mol⁻¹. According to another development, the gasoline fuel composition comprises between 0.01 and 5% by weight of the viscosifying compound. According to a particular embodiment, the gasoline fuel composition further comprises one or more additives selected from detergent additives, anti-valve recession additives, antioxidants and additives for increasing electrical conductivity. The present invention also relates to a method for preparing a gasoline fuel composition comprising dissolving a viscosifying compound at ambient temperature in at least 70% by weight of a liquid gasoline fuel, said viscosifying compound being able to increase the dynamic viscosity of the gasoline fuel up to a dynamic viscosity value greater than or equal to 10 mPa·s, preferably 100 mPa·s, measured at a temperature of 40° C. and at atmospheric pressure, and endow it with a shear-thinning character.

The present invention also relates to a use of a gasoline fuel composition according to the present invention as fuel for the internal-combustion engine of a competition motor vehicle. According to a particular preferred embodiment, the competition motor vehicle weighs less than 1000 kg. According to a particular preferred embodiment, the use of a gasoline fuel composition makes it possible to improve the performance of the competition motor vehicle, preferably the dynamic stability of the competition motor vehicle and/or improve the road holding of the competition motor vehicle, by lowering the average centre of gravity of said vehicle. According to another particular preferred embodiment, the competition motor vehicle comprises a tank intended to contain the fuel consisting of a single cell without subdivision. The present invention further relates to a method of supplying fuel to an internal-combustion engine comprising supplying said engine with a gasoline fuel composition according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features will become clearer from the description that follows. The particular embodiments of the invention are given as non-limitative examples and are represented in the attached drawings in which:

FIG. 1 shows the flow curves for a fuel composition C₁ according to a particular embodiment of the invention, for different temperatures (0, 10, 20, 30 and 40° C.).

FIG. 2 shows the instantaneous viscosity as a function of time for a gasoline fuel composition C₁ according to a particular embodiment of the invention, at a temperature of 20° C.

FIG. 3 shows the instantaneous viscosity as a function of time for a gasoline fuel composition C₁ according to a particular embodiment of the invention, at a temperature of 40° C.

FIG. 4 shows the curve simulating the trajectory along axes x and y, of the centre of gravity of two fuels of different viscosity, Batch 1 and Batch 2 (OpenFOAM-2.2.2 simulation software).

FIG. 5 shows the curve of engine torque as a function of engine speed, obtained from an engine test carried out with gasoline fuel compositions C₀ and C₁ according to a particular embodiment of the invention.

FIG. 6 shows the curve of consumption as a function of engine speed, obtained from an engine test carried out with gasoline fuel compositions C₀ and C₁ according to a particular embodiment of the invention.

DETAILED DESCRIPTION

According to a particular embodiment, a viscosified gasoline fuel composition comprises at least 70% by weight, advantageously at least 85% by weight, preferably at least 90% by weight, more preferably at least 95% by weight, even more preferably at least 98% by weight of a gasoline fuel and at least one viscosifying compound. Fuels of the gasoline type (called gasolines) can be used in spark-ignition engines, naturally aspirated or turbocharged, in particular those of conventional motor vehicles. Fuels of the gasoline type have octane numbers that are high enough to avoid the phenomenon of knock. Typically, the fuels of the gasoline type marketed in Europe, complying with standard EN 228, have a motor octane number (MON) greater than 85 and a research octane number (RON) of at least 95. These fuels of the gasoline type are suitable for the vast majority of car engines. The fuels of the gasoline type according to the invention preferably have a RON greater than or equal to 95 and a MON greater than or equal to 85, the RON and MON being measured according to standard ASTM D 2699-86 or D 2700-86.

According to a particular preferred embodiment, the fuels of the gasoline type are selected from high-power gasoline fuels, in particular the gasoline fuels for motor racing (rallying, circuits) the characteristics of which, currently in force, are stated in article 9.1 of the rules of the International Automobile Federation (FIA) in Appendix J-Art 252, published on Nov. 11, 2010, and are given below:

-   -   For leaded gasolines, i.e. a lead content less than or equal to         0.4 g/L:     -   RON comprised between 97 and 100     -   MON comprised between 86 and 92     -   For unleaded gasolines:     -   RON between 95 and 102     -   MON between 85 and 90         MON and RON are measured according to standard ASTM D 2699-86 or         D 2700-86.     -   Density measured according to standard ASTM D 4052 between 720         and 785 kg/m³     -   Maximum oxygen content below 2.8% by weight or below 3.7% by         weight if the lead content is below 0.013 g/L,     -   Maximum nitrogen content below 0.5% by weight, measured         according to ASTM D 3228,     -   Benzene content below 5% by volume, measured according to         standard ASTM D 3606.

The viscosifying compound is able to increase the viscosity of the gasoline fuel up to a dynamic viscosity value greater than or equal to 10 mPa·s, preferably greater than or equal to 100 mPa·s, measured at a temperature of 40° C. and at atmospheric pressure. The gasoline fuel composition advantageously has a dynamic viscosity comprised between 10 and 50000 mPa·s, preferably between 100 and 1000 mPa·s, more preferably between 100 and 500 mPa·s, at a temperature of 40° C. and at atmospheric pressure. The viscosifying compound is preferably able to increase the dynamic viscosity by a factor greater than or equal to 100, preferably 300, more preferably 800, the dynamic viscosity being measured at a temperature of 40° C., at low shear stress, for example at a shear rate of 0.1 s⁻¹. The content of viscosifying compound necessary for forming a gasoline fuel composition having the required viscosity characteristics can be determined by any known method, in particular by routine tests that are available to a person skilled in the art.

The gasoline fuel composition preferably comprises between 0.01 and 5% by weight of the viscosifying compound, more preferably between 0.05 and 1% by weight, even more preferably between 0.1 and 0.5% by weight. The preferred vicosifying compounds are at least partially soluble in the gasoline fuel at ambient temperature and are able to modify the rheological properties of said fuel. By “partially soluble” is meant that at least 95% by weight of the viscosifying compound is soluble, preferably at least 99% by weight. The viscosifying compound is preferably soluble in the gasoline fuel at ambient temperature, it being understood that solubility may be obtained by any known method.

In particular, the viscosified gasoline fuel composition is prepared by a method that comprises the formation of said composition by dissolving the viscosifying compound at ambient temperature in at least 70% by weight, advantageously at least 85% by weight, preferably at least 90% by weight, more preferably at least 95% by weight, even more preferably at least 98% by weight of a gasoline fuel as described above. Moreover, the viscosifying compound is able to endow the gasoline fuel with a shear-thinning character. Thus, the gasoline fuel composition containing said viscosifying compound is viscoelastic with decrease in viscosity when a mechanical stress applied to said composition increases. The mechanical stress is, for example, a shear stress. The viscosity is measured by any known method.

The viscosified gasoline fuel composition preferably has shear-thinning behaviour under the effect of a mechanical stress between 100 and 1000 s⁻¹, advantageously between 300 and 1000 s⁻¹, more preferably between 500 and 1000 s⁻¹. The viscosified gasoline fuel composition may have shear-thinning behaviour at the yield point, i.e. the viscosified gasoline fuel composition is stable provided it is not subjected to a certain stress, for example a shear stress that corresponds to the yield point. Beyond this threshold (yield point), shear-thinning behaviour is observed.

A critical shear threshold {dot over (γ)}_(C) may be determined, corresponding to a stress value beyond which the viscosified gasoline fuel composition flows with a decrease in dynamic viscosity. This critical shear threshold {dot over (γ)}_(C) defines the limit between the Newtonian or quasi-Newtonian domain of said composition and the shear-thinning domain. Below this threshold value, the gasoline fuel composition is in the viscosified form. For a stress greater than or equal to this threshold value, the viscosity of said composition decreases markedly.

The critical shear threshold {dot over (γ)}_(C) is determined by rheometric measurement and graphical determination. The viscosified gasoline fuel composition preferably has a critical shear threshold, determined by rheometric measurement, below 1000 s⁻¹ at a temperature of 20° C. and at atmospheric pressure, preferably below 500 s⁻¹, more preferably below 100 s⁻¹. For a stress greater than or equal to this threshold value {dot over (γ)}_(C), the viscosity of said composition decreases markedly.

Advantageously, the viscosifying compound is selected from the viscosifying compounds that are able to endow the gasoline fuel with a thixotropic character. The content of viscosifying compound in the gasoline fuel composition is adjusted so that the gasoline fuel composition containing said viscosifying compound advantageously has thixotropic behaviour. The rate of viscosity pickup of the gasoline fuel composition is, advantageously, less than 1 hour, preferably less than 10 min, more preferably less than 1 min. In particular, the rate of viscosity pickup after disappearance of the mechanical stress is advantageously between 0.01 and 3 seconds (instantaneous).

Moreover, the viscosifying compound may be selected from the organogelator compounds capable of forming, with the gasoline fuel, a reversible physical gel that is stable at a temperature less than or equal to 60° C., preferably 40° C., even more preferably 25° C., at a pressure comprised between 1.01 and 1.11 bars. By “physical gel” is meant a gel obtained by reversible formation of a three-dimensional network, by self-assembly of the organogelator compounds via weak interactions of the hydrogen bond type, π-π stacking and/or van der Waals interaction. If at a temperature of 20° C. the gasoline fuel composition is in the form of a gel, under a stress greater than or equal to the threshold value {dot over (γ)}_(C), there is rupture of the gel (destructuring of the three-dimensional network).

By “stable at a temperature” is meant the fact that the gasoline fuel is in the form of a single gel phase. Above this temperature, the gasoline fuel is in the form of a sol phase. The rheological properties of organogels have been studied extensively in the literature. Regarding the characteristics of organogels, reference may be made for example to the articles, Low Molecular Mass Gelators of Organic Liquids, Maity, G. C. 2007, Journal of Physical Sciences, Vol. 11, pp. 156-171; Acc. Chem. Res., George M., Weiss R. G., 2006, 39, 489; Chem. Rev., Steed J. W., Piepenbrock, M-O. M. Lloyd G. O., Clarke N., 2010, 110, 1960.

Advantageously, the organogelator compound will be selected so that in addition it endows the gelled gasoline fuel with a thixotropic character. Thus, after disappearance of the shear stress, the gasoline fuel composition will regain its initial gel structure.

The viscosifying compound is preferably selected from the organogelator compounds capable of forming, with the gasoline fuel, a gel having shear-thinning behaviour on application of:

-   -   a shear stress comprised between 100 and 1000 s⁻¹, preferably         between 300 and 1000 s⁻¹, more preferably between 500 and 1000         s⁻¹     -   in a temperature range less than or equal to 55° C., preferably         30° C., more preferably 25° C., even more preferably 20° C. and,     -   at a pressure comprised between 1.01 and 1.11 bars.

The viscosifying compound may advantageously be selected from the organogelator compounds capable of forming, with the liquid hydrocarbon-containing fuel or combustible, a thermoreversible gel that is stable at a temperature less than or equal to 60° C., preferably 40° C., more preferably 25° C., at a pressure between 1.01 and 1.11 bars. Viscosifying organogelator compounds, forming shear-thinning gels with low molecular weight known by the acronym LMOG (“Low Molecular Weight Organic Gelators), preferably having a molecular weight less than or equal to 2000 g·mol⁻¹, will be selected. These organogelator compounds are known to be capable of modifying the rheological behaviour of organic solvents, while making the gelation reversible since they are very sensitive to shearing. By way of example there may be mentioned, the article “Low Molecular Mass Gelators of Organic Liquids and the Properties of Their Gels” by Terech, P. and Weiss, R. G. 1997, Chem. Rev., Vol. 97, pp. 3133-3159.

According to a particular embodiment, the viscosifying compound is selected from the organogelator compounds derived from ureas and bis-ureas, alone or in a mixture, preferably from the derivatives of the N-substituted ureas and N-substituted bis-ureas, symmetric or asymmetric, alone or in a mixture. The viscosifying compound may advantageously be selected from the organogelator compounds derived from the N-substituted bis-ureas, symmetric or asymmetric, preferably asymmetric, alone or in a mixture. So that the viscosifying compound is soluble in the gasoline fuel, it may advantageously comprise a substituent that compatibilizes the viscosifying compound with the gasoline fuel. This substituent may be of an aromatic nature and/or a non-polar aliphatic nature.

Advantageously, the viscosifying compound comprises at least one substituent borne by a nitrogen atom of a urea function of the viscosifying compound. The substituent is selected from the group consisting of the C₅ to C₁₀ monocyclic or polycyclic aromatic rings, C₅ to C₁₀ heterocyclic rings, preferably the C₅-C₆ monocyclic aromatic rings, optionally substituted with one or more linear or branched, saturated or unsaturated, C₁ to C₁₀ hydrocarbon-containing chains, preferably C₁ to C₄, said chains optionally containing one or more heteroatoms selected from N, O and S. The viscosifying compound preferably comprises at least one substituent borne by a nitrogen atom of a urea function of the viscosifying compound. The substituent is selected from the group consisting of the linear or branched C₁ to C₂₄ hydrocarbon-containing chains, saturated or unsaturated, even more preferably C₃ to C₁₀, said chains optionally containing one or more heteroatoms selected from N, O and S.

According to a particular embodiment, the viscosifying compound is represented by the following formula (1):

in which: R₁ and R₂, are identical or different, represent independently a group selected from the group consisting of:

-   -   linear or branched, saturated or unsaturated C₁ to C₂₄         hydrocarbon-containing chains, preferably C₃ to C₁₆, even more         preferably C₆ to C₁₂, said chains optionally containing one or         more heteroatoms selected from N, O and S and/or one or more C₅         to C₁₀ monocyclic or polycyclic aromatic rings, preferably C₅ or         C₆ monocyclic aromatic rings, and     -   C₅ to C₁₀ monocyclic or polycyclic aromatic rings, C₅ to C₁₀         heterocyclic rings, preferably C₅-C₅ monocyclic aromatic rings,         optionally substituted with one or more linear or branched,         saturated or unsaturated C₁ to C₁₀ hydrocarbon-containing         chains, preferably C₁ to C₄, said chains optionally containing         one or more heteroatoms selected from N, O and S.

According to another particular embodiment, the viscosifying compound is represented by the following formula (2):

in which: Y represents a group selected from the group consisting of:

-   -   C₅ to C₁₀ monocyclic or polycyclic aromatic rings, C₅ to C₁₀         heterocyclic rings, preferably C₅-C₆ monocyclic aromatic rings,         optionally substituted with one or more linear or branched,         saturated or unsaturated C₁ to C₁₀ hydrocarbon-containing         chains, preferably C₁ to C₄, said chains optionally containing         one or more heteroatoms selected from N, O and S,     -   linear or branched, saturated or unsaturated C₁ to C₂₄         hydrocarbon-containing chains, preferably C₃ to C₁₈, even more         preferably C₆ to C₁₂, said chains optionally containing one or         more heteroatoms selected from N, O and S,         R₃ and R₄, are identical or different, represent independently a         group selected from the group consisting of linear or branched,         saturated or unsaturated C₁ to C₂₄ hydrocarbon-containing         chains, preferably C₃ to C₁₈, even more preferably C₆ to C₁₂,         said chains optionally containing one or more heteroatoms         selected from N, O and S and/or one or more C₅ to C₁₀ monocyclic         or polycyclic aromatic rings, preferably C₅ or C₆ monocyclic         aromatic rings.         Y represents, advantageously, a group selected from the group         consisting of C₅ to C₁₀ monocyclic or polycyclic aromatic rings,         C₅ to C₁₀ heterocyclic rings, preferably C₅-C₆ monocyclic         aromatic rings, optionally substituted with one or more linear         or branched, saturated or unsaturated C₁ to C₁₀         hydrocarbon-containing chains, preferably C₁ to C₄, said chains         optionally containing one or more heteroatoms selected from N, O         and S.

Advantageously, R₃ and R₄, are identical or different, represent independently a group selected from the group consisting of linear or branched, saturated or unsaturated C₁ to C₂₄ hydrocarbon-containing chains, cyclic or acyclic, said chains optionally containing one or more heteroatoms selected from N, O and S in the form of one or more functions selected from the ether, ester, ketone, amine, amide, imine, thiol, thioether or thioester functions and/or one or more C₅ to C₁₀ monocyclic or polycyclic aromatic rings, preferably C₅ or C₆ monocyclic aromatic rings, optionally substituted with one or more linear or branched, saturated or unsaturated C₁ to C₁₀ hydrocarbon-containing chains, preferably C₁ to C₄. According to a development, R₃ and R₄, are identical or different, represent independently the —CH(R₆)COOR₇ group in which:

R₆ and R₇, are identical or different, are selected independently from the group consisting of linear or branched, saturated or unsaturated, cyclic or acyclic C₁ to C₂₄ hydrocarbon-containing chains, preferably C₁ to C₁₅, said chains optionally containing one or more C₅ to C₁₀ monocyclic or polycyclic aromatic rings, preferably C₅ or C₆ monocyclic aromatic rings, optionally substituted with one or more linear or branched, saturated or unsaturated C₁ to C₁₀ hydrocarbon-containing chains, preferably C₁ to C₄. R₆ or R₇ may, for example, be selected from the group consisting of the methyl, ethyl, propyl, butyl, t-butyl, phenyl, tolyl, xylyl, benzyl, 3,7-dimethyl-octyl, 2-hexyl-decyl oleyl 2-hexyl-decyl, 2-butyl-octyl, farnesyl, 1-dodecyl, 2-dodecyl, cyclododecyl-methyl, 2-ethyl-1-hexyl radicals.

According to another particular preferred embodiment, the viscosifying compound is represented by the following formula (3):

in which: R₃ and R₄ are as described above and R₅ represents a group selected from the group consisting of linear or branched C₁ to C₁₂ hydrocarbon-containing chains, preferably C₁ to C₆, more preferably C₁ to C₃, even more preferably C₁.

By way of example of an organogelator compound, there may be mentioned N,N′-2,4-bis((2-ethylhexyl) ureido) toluene (EHUT) corresponding to formula (3) in which R₃ and R₄ are a 2-ethyl-hexyl substituent and R₅ is a methyl substituent. The organometallic compounds are, preferably, excluded from the list of viscosifying compounds covered by the present invention.

Moreover, the viscosified gasoline fuel composition may comprise one or more other additives different from the viscosifying compound according to the invention. In particular, the gasoline fuel composition may comprise at least one detergent additive, known per se, ensuring cleanness of the admission circuit. Other additives may also be incorporated into the fuel compositions according to the invention, such as anti-valve recession additives and antioxidants.

In order to ensure maximum safety during refuelling, it is also preferable that the electrical conductivity of the fuel is greater than 200 pS/m. For this purpose, at least one additive that increases the electrical conductivity may be added.

The viscosifying compounds described above may be added to the hydrocarbon compositions in the refinery, and/or may be incorporated downstream of the refinery, optionally mixed with other additives, in the form of an additive package. The use of a viscosifying compound is particularly advantageous when the viscosifying compound is also able to impart a thixotropic character to the gasoline fuel composition.

Thus, for example, during pumping of the viscosified gasoline fuel composition in the fuel system of a motor vehicle tank, said composition is subject to an approximate gradient of shear rate customarily between 650 and 1000 s⁻¹. The viscosity of the composition falls during pumping to a value compatible with engine operation. The proportion of the gasoline fuel composition not consumed by the engine and recirculated regains its initial viscosity in the tank in the absence of shear stresses, by the thixotropic effect.

The viscosified gasoline fuel composition is particularly advantageous in that it can be used directly in a method for supplying fuel to an internal-combustion engine. The method comprises, in particular, supplying said engine with the viscosified gasoline fuel composition by any known method. The applicant discovered that the viscosified, preferably gelled, gasoline fuel composition according to the invention makes it possible to improve the performance of a competition vehicle. In particular, the use of a viscosified gasoline fuel composition as described above is particularly advantageous as fuel for the internal-combustion engine of a competition motor vehicle.

A competition motor vehicle generally weighs less than 1000 kg, preferably less than 700 kg, more preferably between 600 and 700 kg. Moreover, a competition motor vehicle generally comprises a tank intended to contain the fuel. Conventionally, the tank is connected to the internal-combustion engine so as to feed a combustion chamber of said engine.

It has been demonstrated that the viscosified gasoline fuel composition makes it possible to improve the performance of a competition motor vehicle. In particular, the use of the viscosified gasoline fuel composition described above makes it possible to improve the dynamic stability of the competition motor vehicle. The gain has an effect, in particular, on the lap time, with an increase in cornering speed.

The gasoline fuel composition stored in the tank of the competition motor vehicle moves by inertia and will strike the walls of the tank. This movement generates forces that will oppose the change of direction or acceleration of the competition motor vehicle. If the gasoline fuel composition is viscosified, i.e. thickened, the amplitude of these forces originating from the movement of the gasoline fuel composition will be decreased or even cancelled, thus improving the dynamic stability of the competition motor vehicle.

The use of the viscosified gasoline fuel composition described above also makes it possible to improve the road holding of the competition motor vehicle, by lowering the average centre of gravity of the vehicle. The road holding of a competition vehicle depends on the centre of gravity of said vehicle: the lower it is, the better the road holding. Now, the level of a viscosified gasoline fuel composition in the tank of a vehicle remains much more horizontal than that of the same gasoline fuel composition that is not viscosified. The increase in viscosity of the gasoline fuel composition leads to a lowering of the centre of gravity of said composition, and therefore lowers the centre of gravity of the competition motor vehicle.

Moreover, the use of a viscosified gasoline fuel composition as described above makes it possible to limit the unbalance of a fuel composition in the tank of a competition vehicle of the Formula 1 type. At present, the only technical solution for limiting excessive unbalance of a fuel composition in the tank of a competition vehicle of the Formula 1 type is to subdivide the tank into smaller cells connected together, so that the movement of the fuel composition under the effect of the different accelerations takes place over a shorter distance and weight (over the length of a cell). Now, the gasoline fuel composition represents on average between 10 and 20% of the weight of a competition vehicle at the start of the race (generally between 640 and 690 kg). A competition motor vehicle generally weighs less than 1000 kg. This subdivision system weighs about 1500 grams and therefore has the drawback of a weight disadvantage for the competition vehicle (0.15% of vehicle weight).

According to a particular embodiment, the competition motor vehicle comprises a tank intended to contain the fuel consisting of a single cell without subdivision. Use of the viscosified gasoline fuel composition described above allows a weight gain of the competition motor vehicle by eliminating the internal cells of the tank of said vehicle and actually improves the performance of the competition motor vehicle, in particular the speed of said vehicle.

The potential gain with the viscosified gasoline fuel composition is estimated at a total gain of at least 0.13 s/rev, preferably at least 0.2 s/rev. This gain of 0.2 s/rev represents a substantial gain in the context of competition races.

EXAMPLE Preparation of a Gasoline Fuel Composition C₁

A gasoline fuel composition denoted C₁ is prepared by dissolving 7000 ppm by weight of N,N′-2,4-bis((2-ethylhexyl)ureido) toluene (EHUT) in a competition gasoline fuel of the Formula 1 type, denoted C₀, with magnetic stirring, for 4 h. The characteristics of the gasoline fuel C₀ are listed in Tables 1 and 2 below:

TABLE 1 Results of analysis by high-resolution gas chromatography for determining the percentages by volume of the paraffin, olefin, naphthene and aromatic compounds according to the standard test ASTM 6730, said analysis being known as PONA analysis, and results of the analysis for determining the percentages by volume of the saturated or unsaturated oxygenated compounds by gas chromatography coupled to a flame ionization detector (GC-FID) Fuel C₀ % by volume Paraffins 42.0 Olefins 18.4 Naphthenes 18.7 Aromatics 7.6 Saturated oxygens 13.2

TABLE 2 Physical characteristics of gasoline fuel C₀ Measurements Methods Units Results Octane numbers ASTM D 2699-86 MON 87.5 ASTM D 2700-86 RON 97.9 Density ASTM D 4052 kg/l 0.715 Reid vapour EN ISO 13016 mbar 519 pressure E70° C. ASTM D86 % v/v 41.3 E100° C. ASTM D86 % v/v 96.2

Dynamic Viscosity of Gasoline Fuel C₀

Measurements of kinematic viscosity as a function of temperature were carried out on a sample of the gasoline fuel composition C₀ alone, on a tube viscosimeter according to standard EN 3104. The results were then corrected to each temperature of the density of the gasoline fuel composition C₀.

The results are listed in Table 3 below:

TABLE 3 C₀ Temperature Composition (° C.) (Pa · s) 10 4.36 × 10⁻⁴ 20 3.94 × 10⁻⁴ 30 3.60 × 10⁻⁴ 40 3.33 × 10⁻⁴

Rheological Properties of the Gasoline Fuel Composition C₁

The rheological characterizations of the gasoline fuel composition C₁ were carried out with a flat cone geometry with an angle of 2° and a diameter of 60 mm, with temperature control using a Peltier device.

Flow Behaviour

As shown in FIG. 1, the variation of the viscosity of the gasoline fuel composition C₁ is plotted as a function of the shear rate. The flow curves are obtained by logarithmic variation of the shear rate from 0.01 to 100 s⁻¹ for each temperature, 0° C., 10° C., 20° C., 30° C. and 40° C.

The viscosity results obtained at a shear rate of 0.01 s are compared with the measurements of kinematic viscosities of gasoline fuel C₀ in Table 4 below:

TABLE 4 Dynamic Dynamic viscosity viscosity Viscosity Temperature Composition Fuel C₁ ratio (° C.) C₀ (Pa · s) (Pa · s) C₁/C₀ 10 4.36 × 10⁻⁴ 1.8 4129 20 3.94 × 10⁻⁴ 1.00 2536 30 3.60 × 10⁻⁴ 0.50 1388 40 3.33 × 10⁻⁴ 0.30 901

The presence of the organogelator compound EHUT in the gasoline fuel composition C₁ increases the viscosity by a factor from about 900 to about 4000, at low shear, compared to gasoline fuel composition C₀ without the organogelator compound EHUT. At ambient temperature, composition C₁ is in the form of a gel.

As shown in FIG. 1, a marked decrease in viscosity of the gasoline fuel composition C₁ with the increase in temperature is observed regardless of the shear rate. At temperatures of 0, 10 and 20° C., similar to storage temperatures in a tank of a vehicle equipped with an engine operating with the gasoline fuel compositions, the viscosity is higher than at temperatures of 30 and 40° C. corresponding to the temperatures of use. By “temperatures of use” is meant the temperatures encountered in the fuel system of the combustion engine of a motor vehicle.

Moreover, the curves obtained reflect shear-thinning behaviour at the yield point of the gasoline composition C₁. For each temperature, a first quasi-Newtonian plateau is observed for the low values of the shear rate, in particular for the values of the shear rate below 0.1 s⁻¹.

The viscosity remains constant up to a critical shear threshold {dot over (γ)}_(C). Starting from the critical shear threshold {dot over (γ)}_(C) the value of the viscosity decreases rapidly, tending towards a second quasi-Newtonian plateau. The value of the critical shear threshold {dot over (γ)}_(C) can be determined graphically for each temperature. The results are listed in Table 5 below:

TABLE 5 Temperature Critical shear [° C.] threshold {dot over (γ)}_(C) [s⁻¹] 0 0.02 10 0.1 20 0.8 30 1 40 1

For shear rates greater than 100 s⁻¹, generally corresponding to the gradient of the rate imposed by a circulating pump, also called booster pump of a conventional combustion engine, the viscosity of fuel composition C₁ changes from 1 Pa·s to about 0.05 Pa·s (at 20° C.). During circulation of fuel composition C₁ in the fuel system of a combustion engine, the mechanical stresses imposed on the fuel composition C₁ destructure the three-dimensional network formed by the organogelator compound EHUT within said composition. Thus, under the conditions of use, the viscosity falls to a low viscosity value, compatible with the operating conditions of a combustion engine. By “conditions of use” is meant the conditions to which the fuel composition is subjected in the fuel systems of a combustion engine of a motor vehicle. The shear-thinning character of the fuel composition C₁ according to the present invention avoids any risk of disturbance of the circulation of the fuel composition C₁ in the fuel system of the tank while maintaining the advantages of high viscosity of said gasoline fuel composition at the storage temperatures in the tank.

Creep/Recovery Test

At a given temperature, a shear rate of 500 s⁻¹ is applied for 2 min. This rate must be high enough to ensure destructuring of the fuel composition C₁ at a given temperature. Then the pickup in dynamic viscosity is observed at a low shear rate of 0.1 s⁻¹. The restructuring was monitored by oscillation measurements at a frequency of 1 Hz and an amplitude of 1 Pa. The measurements are carried out at a temperature of 20 and 40° C.

As shown in FIGS. 2 and 3, regardless of the measurement temperature, viscosity pickup is almost immediate (1 to 2 seconds) after a decrease in shear rate. As shown in FIG. 3, under the conditions of preparation of the sample at 20° C., viscosity pickup is almost immediate at 0.2 Pa·s and then it stabilizes at a maximum value of 0.5 Pa·s after about 15 minutes. As shown in FIG. 4, the behaviour of the gasoline fuel composition C₁ is similar at 40° C., with a viscosity pickup/upturn after 15 minutes and a maximum value of viscosity equal to 0.3 Pa·s.

These creep/recovery tests reflect a thixotropic behaviour of the gasoline fuel composition C₁. The gasoline fuel composition according to the present invention has a thixotropic character, reflecting a high capacity for restructuring. Now, the tank bottom booster pumps of a motor vehicle have a flow rate such that they generally supply a quantity of fuel composition of up to double the quantity consumed by the combustion engine. Thus, a high proportion of the gasoline fuel composition is returned to the tank after passing through a booster pump.

Thus, as the gasoline fuel composition C₁ is no longer subjected to shear stresses after re-circulation, in the tank it regains greater consistency with respect to an increase in its viscosity. The thixotropic character of the fuel composition C₁ according to the present invention avoids any risk of disturbing the circulation of the fuel composition C₁ in the fuel system of the tank, while maintaining the advantages of high viscosity of said gasoline fuel composition at the storage temperatures in the tank.

Numerical Simulation of the Hydrodynamic Behaviour of Gasoline Fuel Compositions as a Function of their Viscosity

The OpenFOAM-2.2.2 software was used for simulating the behaviour of two fuels denoted Batch 1 and Batch 2, of different viscosity, subjected to a high deceleration of force 3G in a cubic tank with 600 mm side containing 72 litres of fuel at rest. In particular, the trajectory of the centre of gravity of the liquid was simulated along the x and y axes (FIG. 4). A two-phase Solver of the VOF (“Volume Of Fluid”) type, unsteady, with a turbulence model of the RANS type, was used.

The characteristics adopted for this simulation are as follows:

-   -   Geometry and the mesh of the tank: 1 million cubic cells with 6         mm side     -   Batch 1: Newtonian fluid with a constant viscosity of 4.36×10⁻⁴         Pa·s (compressible model)     -   Batch 2: Newtonian fluid with a viscosity depending on the shear         rate (incompressible model). An interpolation method was added         to the solver in order to vary the viscosity of the numerical         model as a function of the shear rate. The interpolation         function applied in order to calculate the viscosity at each         cell of the mesh according to the local value of the shear rate         is deduced from the viscosity curve as a function of the shear         rate at 10° C. obtained from FIG. 1.     -   Density of the fluids: 790 kg·m⁻³     -   Gravitational acceleration: an interpolation method was added to         the solver in order to vary the gravitational constant of the         numerical model as a function of time. The initial gravitational         constant has a value of         =(3 g, 0, −g) with g=9.81 m·s⁻². A deceleration is then applied         linearly along the x axis for a duration of 1 second, such that         =(0, 0, −g).

As shown in FIG. 4, the trajectory of the centre of gravity of Batch 1 shows a larger amplitude than that of Batch 2. The relative difference in amplitude along the y axis is calculated between Batch 2 and Batch 1. The result is presented in Table 6 below:

TABLE 6 Δ z_(max) (z_(max Batch 2) − z_(max Batch 1))/z_(max Batch 1) (m) (%) Batch 1 0.3957 — Batch 2 0.3404 −14

A reduction in the maximum amplitude of the movement of the centre of gravity is therefore observed. Thus, this simulation confirms that increasing the viscosity of the gasoline fuel composition leads to a lowering of the centre of gravity of the motor vehicle. The unbalance of said composition in the tank of a vehicle is limited, compared to a composition that has not been viscosified. It is deduced from this that the dynamic stability is consequently improved, with better road holding of the vehicle and increased lap speed and/or cornering speed.

Engine Safety Test

An engine test was carried out with the gasoline fuel compositions C₀ and C₁ in order to evaluate the effect of viscosification, in particular gelation, on correct engine operation. The engine used is a Renault H5Ft four-cylinder engine, 1.2-litre capacity (1198 cm³), with a power of 115 HP, turbocharged and equipped with a direct injection system capable of delivering a flow at 150 bars. The engine is used at full load from 1000 to 5500 rpm in steps of 500 rpm. The values of engine torque obtained as a function of engine speed are shown in FIG. 5 and the consumption values obtained as a function of engine speed are shown in FIG. 6.

At 2 sigmas, the repeatability of measurement is ±3 Nm for the measurements of engine torque (FIG. 5) and 0.25 kg/h for the measurements of consumption (FIG. 6). As shown in FIGS. 5 and 6, viscosification, in particular gelation of gasoline does not affect correct engine operation. In fact, it can be seen that the gasoline fuel compositions C₀ and C₁ induce almost identical responses both with respect to the values of engine torque (FIG. 5) or of consumption (FIG. 6) as a function of engine speed. 

1. A gasoline fuel composition comprising at least 70% by weight of a gasoline fuel and at least one viscosifying compound able to increase the dynamic viscosity of the gasoline fuel up to a dynamic viscosity value greater than or equal to 10 mPa·s measured at a temperature of 40° C. and at atmospheric pressure and endow it with a shear-thinning character.
 2. The composition according to claim 1, wherein the composition has shear-thinning behaviour on application of a stress of between 100 and 1000 s⁻¹.
 3. The composition according to claim 1, wherein the viscosifying compound is selected from the viscosifying compounds able to endow the composition with a thixotropic character.
 4. The composition according to claim 1, wherein the viscosifying compound is selected from the derivatives of the N-substituted ureas and N-substituted bis-ureas, symmetric or asymmetric, alone or in a mixture.
 5. The composition according to claim 4, wherein the viscosifying compound is selected from the derivatives of the N-substituted bis-ureas, symmetric or asymmetric, alone or in a mixture.
 6. The composition according to claim 4, wherein the viscosifying compound comprises at least one substituent borne by a nitrogen atom of a urea function of the viscosifying compound, the substituent being selected from the group consisting of the C₅ to C₁₀ monocyclic or polycyclic aromatic rings, C₅ to C₁₀ heterocyclic rings, optionally substituted with one or more linear or branched, saturated or unsaturated C₁ to C₁₀ hydrocarbon-containing chains, the chains optionally containing one or more heteroatoms selected from N, O and S.
 7. The composition according to claim 4, wherein the viscosifying compound comprises at least one substituent borne by a nitrogen atom of a urea function of the viscosifying compound, the substituent being selected from the group consisting of the linear or branched, saturated or unsaturated C₁ to C₂₄ hydrocarbon-containing chains, the chains optionally containing one or more heteroatoms selected from N, O and S.
 8. The composition according to claim 1, wherein the viscosifying compound is represented by the following formula (1):

wherein R₁ and R₂, are identical or different, represent independently a group selected from the group consisting of: (a) linear or branched, saturated or unsaturated C₁ to C₂₄ hydrocarbon-containing chains, the chains optionally containing one or more heteroatoms selected from N, O and S and/or one or more C₅ to C₁₀ monocyclic or polycyclic aromatic rings, and (b) C₅ to C₁₀ monocyclic or polycyclic aromatic rings, C₅ to C₁₀ heterocyclic rings, optionally substituted with one or more linear or branched, saturated or unsaturated C₁ to C₁₀ hydrocarbon-containing chains, the chains optionally containing one or more heteroatoms selected from N, O and S.
 9. The composition according to claim 1, wherein the viscosifying compound is represented by the following formula (2):

wherein: Y represents a group selected from the group consisting of: (a) C₅ to C₁₀ monocyclic or polycyclic aromatic rings, C₅ to C₁₀ heterocyclic rings, optionally substituted with one or more linear or branched, saturated or unsaturated C₁ to C₁₀ hydrocarbon-containing chains, the chains optionally containing one or more heteroatoms selected from N, O and S, (b) linear or branched, saturated or unsaturated, C₁ to C₂₄ hydrocarbon-containing chains the chains optionally containing one or more heteroatoms selected from N, O and S, R₃ and R₄, are identical or different, represent independently a group selected from the group consisting of linear or branched, saturated or unsaturated C₁ to C₂₄ hydrocarbon-containing chains, the chains optionally containing one or more heteroatoms selected from N, O and S and/or one or more C₅ to C₁₀ monocyclic or polycyclic aromatic rings.
 10. The composition according to claim 9, wherein Y represents a group selected from the group consisting of C₅ to C₁₀ monocyclic or polycyclic aromatic rings, C₅ to C₁₀ heterocyclic rings, optionally substituted with one or more linear or branched, saturated or unsaturated C₁ to C₁₀ hydrocarbon chains, the chains optionally containing one or more heteroatoms selected from N, O and S.
 11. The composition according to claim 9, wherein R₃ and R₄, are identical or different and represent independently a group selected from the group consisting of linear or branched, saturated or unsaturated, cyclic or acyclic, C₁ to C₂₄ hydrocarbon-containing chains, the chains optionally containing one or more heteroatoms selected from N, O and S in the form of one or more functions selected from the ether, ester, ketone, amine, amide, imine, thiol, thioether or thioester functions and/or one or more C₅ to C₁₀ monocyclic or polycyclic aromatic rings, optionally substituted with one or more linear or branched, saturated or unsaturated C₁ to C₁₀ hydrocarbon-containing chains.
 12. The composition according to claim 9, wherein R₃ and R₄, are identical or different and represent independently the —CH(R₆)COOR₇ group wherein R₆ and R₇, are identical or different, are selected independently from the group consisting of linear or branched, saturated or unsaturated, cyclic or acyclic C₁ to C₂₄ hydrocarbon-containing chains, the chains optionally containing one or more C₅ to C₁₀ monocyclic or polycyclic aromatic rings, optionally substituted with one or more linear or branched, saturated or unsaturated C₁ to C₁₀ hydrocarbon-containing chains.
 13. The composition according to claim 9, wherein the viscosifying compound is represented by the following formula (3):

wherein R₃ and R₄ are as defined in claim 9 and R₅ represents a group selected from the group consisting of linear or branched C₁ to C₁₂ hydrocarbon-containing chains.
 14. The composition according to claim 1, wherein the viscosifying compound has a molecular weight less than or equal to 2000 g·mol⁻¹.
 15. The composition according to claim 1, wherein it comprises between 0.01 and 5% by weight of the viscosifying compound.
 16. The composition according to claim 1, further comprising one or more additives selected from detergent additives, anti-valve recession additives, antioxidants and additives for increasing electrical conductivity.
 17. A method for preparing a gasoline fuel composition, the method comprising dissolving, at ambient temperature, a viscosifying compound in at least 70% by weight of a liquid gasoline fuel, the viscosifying compound increasing a dynamic viscosity of the gasoline fuel up to a dynamic viscosity value greater than or equal to 10 mPa·s, measured at a temperature of 40° C. and at atmospheric pressure, and endowing the gasoline fuel with a shear-thinning character. 18-23. (canceled)
 24. A method of supplying fuel to an internal-combustion engine comprising supplying the engine with the gasoline fuel composition according to claim
 1. 25. A method comprising improving performance of a vehicle with an internal-combustion engine by supplying the engine with a gasoline fuel composition comprising at least 70% by weight of a gasoline fuel and at least one viscosifying compound able to increase the dynamic viscosity of the gasoline fuel up to a dynamic viscosity value greater than or equal to 10 mPa·s measured at a temperature of 40° C. and at atmospheric pressure, and endowing it with a shear-thinning character.
 26. The method according to claim 25, wherein the vehicle is a competition motor vehicle.
 27. The method according to claim 26, wherein the competition motor vehicle comprises a tank intended to contain the fuel including a single cell without subdivision.
 28. The method according to claim 25, further comprising improving dynamic stability of a competition motor vehicle with the internal-combustion engine by the supplying the engine with the gasoline fuel composition, wherein the competition motor vehicle weighs less than 1000 kg.
 29. The method according to claim 25, further comprising improving road holding of a competition motor vehicle, by lowering an average center of gravity of the vehicle and wherein the competition motor vehicle weighs less than 1000 kg. 